Now that summer’s in full swing, it’s time to make sure you’re fully protected from sun. But what kind of sunscreen should you buy? How long should you keep it? And just what are the factors for skin cancer anyway? In this special feature, we answer the top myths about sunscreen, bring you a top dermatologist’s sunscreen recommendations, and offer a quick way for you to assess your own chances of getting skin cancer.

Top Sunscreen Myths

1. The higher the SPF, the better the protection.

FALSE. It sounds right — a sun protection factor of 100 should be twice as protective as SPF 50. But it’s only a few percentage points more effective. An SPF of 15 screens 93% of the sun’s rays and an SPF of 30 screens 97%. “But the number becomes irrelevant if you aren’t applying enough in the first place,” says Mona Gohara, MD, a dermatologist in Danbury, Conn., and an assistant clinical professor at Yale University Department of Dermatology. Studies show the average person slaps on one-seventh to one-tenth of the amount of SPF needed to reach the number that’s on the bottle.

“For better protection apply 1 to 2 ounces (the size of a Ping-Pong ball) of sunscreen on your body 30 minutes before going outdoors [so your skin can absorb it completely], and every two hours to any exposed skin after that,” Gohara says. For your face, apply a dollop the size of a silver dollar every day, no matter what the weather. Note, too, that SPF refers to protection from UVB (the burning rays) only, not UVA (the aging rays). You need to guard against both, since both can lead to skin cancer.

2. It’s OK to use last year’s bottle of SPF.

TRUE. Most sunscreens have a shelf life of about two years, says Jordana Gilman, MD, a New York City dermatologist. If you are using sunscreen properly, however, you shouldn’t have any left, since it takes about 1 to 2 ounces of sunscreen to cover the entire body, so a 4-ounce bottle should last for only four applications.

3. Sunscreen only needs to be applied to exposed skin.

FALSE. The average T-shirt offers an SPF of about 7, notes Gilman. Darker fabrics and tighter weaves provide more protection, but it is much safer to apply sunscreen to your entire body before you get dressed. Or better yet, wear clothing made of UV protective fabrics. These have been specially treated with colorless UV-absorbing dyes, and most offer an ultraviolet protection factor (UPF) of 50, which blocks both UVA and UVB.

Don’t want to invest in a whole new summer wardrobe? Spike your detergent with a wash-in SPF product you can toss in with your laundry.

4. Using makeup with SPF is just like wearing regular facial sunscreen.

FALSE. Certainly, applying makeup that contains SPF is better than skipping it altogether, but it’s not as effective as wearing a facial lotion with sunscreen underneath. Generally, most makeup cracks on skin, allowing UV rays through. “For makeup to provide adequate ultraviolet protection, it would need to be applied in a really thick layer, which most women do not do,” Gilman says. So unless you plan to spackle on your foundation, smooth on a layer of lotion with sunscreen first, and then apply your makeup.

5. Sunscreen can cause cancer.

FALSE. The only way sunscreen could be hazardous to your health is if it is absorbed into the body, which does not happen, says Amy Wechsler, MD, dermatologist and author of The Mind-Beauty Connection: 9 Days to Reverse Stress Aging and Reveal More Youthful, Beautiful Skin. “UV rays break down the chemical molecules in some sunscreens relatively quickly, long before they can seep into skin.”

Still concerned? Use a sunscreen containing physical blocking ingredients such as zinc oxide and titanium oxide, which stay on the surface of the skin as a protective barrier. Don’t be tempted to use babies’ or children’s sunscreens, which don’t necessarily contain physical blocks. And make sure to check the “active ingredients” section on the label to see what the bottle contains. Even the same product can vary from year to year. Some dermatologists believe people should wear physical blocks only. They might be safer than a mix but are harder to find and not as easy to wear since they tend to be thicker and goopier products. Try a few to find one you like.

6. “Waterproof” sunscreen doesn’t need to be reapplied after swimming.

FALSE. It’s no surprise researchers at the Colorado School of Public Health recently found that vacations near the water were associated with a 5% increase in small skin moles, which in turn boosts a person’s risk of melanoma. While the FDA recognizes the term “water resistant” (which means a sunscreen offers SPF protection after 40 minutes of exposure to water), it does not acknowledge the term “waterproof.” “No sunscreen is truly waterproof,” Wechsler confirms. Sunscreen should be reapplied every two to three hours — and every time you get out of the water if you’re doing laps in the pool or splashing around in the ocean.

7. Wearing sunscreen can lead to vitamin D deficiency.

FALSE. There’s no denying that our bodies need vitamin D (which can be obtained though sun exposure) to function — without it, the body can’t use calcium or phosphorus (minerals necessary for healthy bones). And according to a study published in Archives of Internal Medicine, three-quarters of Americans are deficient in the crucial vitamin. But that doesn’t give you a no-SPF pass. “You still get enough sun to make plenty of vitamin D through the sunscreen,” says Brett Coldiron, MD, a dermatologist at the University of Cincinnati. If you’re worried about vitamin D deficiency leading to brittle bones, Wechsler says, ask your doctor about taking a supplement. The Institute of Medicine’s recently revised guidelines recommend most adults get 600 international units of vitamin D a day; some people may need more.

8. Sunscreen with antioxidants provides better UVA/UVB protection.

TRUE. While they aren’t necessarily active sunscreen ingredients, antioxidants are great SPF supplements. Sunscreen alone does not block all of the damaging rays from the sun — even an SPF of 50 blocks out only 98% of UV rays. “Antioxidants are a good way to catch the UV radiation that ‘sneaks’ past the sunscreen,” Gohara says. Sunscreens infused with antioxidants such as skin-loving green tea extract or polyphenols from tomatoes and berries are proven to reduce the formation of free radicals (small chemical particles that wreak havoc on skin and can cause skin cancer) in the presence of UV light.

NEW YORK (Reuters Health) – Men who consume the recommended amount of vitamin D are somewhat less likely to suffer a heart attack or stroke than those who get little of the vitamin in their diets, a large U.S. study suggests.

Following nearly 119,000 adults for two decades, researchers found that men who got at least 600 international units (IU) of vitamin D each day — the current recommended amount — were 16 percent less likely to develop heart problems or a stroke, versus men who got less than 100 IU per day.

There was no such pattern among women, however, the researchers report in the American Journal of Clinical Nutrition.

The authors say the findings do not prove that vitamin D, itself, deserves the credit for the lower risks seen in men. So they should not start downing supplements for the sake of their hearts.

“The evidence is not strong enough yet to make solid recommendations,” said lead researcher Dr. Qi Sun, a research associate at the Harvard School of Public Health.

On the other hand, the apparent benefits were linked to vitamin D intakes near what’s already recommended: Last year, the Institute of Medicine (IOM), a scientific advisory panel to the U.S. government, bumped up the recommended dose to 600 IU for most people. Adults older than 70 were told to get 800 IU.

So these latest findings may encourage more people to meet those guidelines, Sun said.

But as far as whether vitamin D cuts heart disease and stroke risk, the jury is still out.

Sun said that more answers should come from an ongoing clinical trial that is looking at whether a high dose of vitamin D (2,000 IU per day) can cut the risk of heart disease, stroke and other chronic diseases.

Clinical trials, wherein people are randomly assigned to a treatment or a placebo, are considered the “gold standard” of medical evidence.

So far, there have been few such randomized clinical trials testing vitamin D’s health effects.

A flurry of studies in recent years has linked higher vitamin D intake to lower risks of everything from diabetes, to severe asthma, heart disease, certain cancers and depression.

The problem with those studies is that were “observational” — researchers looked at people’s vitamin D intake, or their blood levels of the vitamin, and whether they developed a given health condition. Those kinds of studies cannot prove cause-and-effect.

The current study was also observational, based on data from two long-term projects that have followed two large groups of U.S. health professionals since the 1980s.

Out of 45,000 men, there were about 5,000 new cases of cardiovascular disease over the study period. These were defined by an incident of heart attack, stroke, or death attributed to cardiovascular disease.

After accounting for a range of factors — like age, weight, exercise levels and other diet habits, such as fat intake – Sun’s team found that men who got at least 600 IU of vitamin D from food and supplements had a 16 percent lower risk of heart attack and stroke compared to men who got less than 100 IU of vitamin D per day.

For women, though, there was no correlation between vitamin D intake and cardiovascular health.

It’s not clear why that is, Sun said. One possibility is that women may have less active vitamin D circulating in the blood; vitamin D is stored in fat, and women typically have a higher percentage of body fat than men do.

But more research is needed, Sun said, to know whether real biological differences underlie the current findings.

In theory, vitamin D could help ward off heart disease and stroke; lab research suggests that it may help maintain healthy blood vessel function and blood pressure levels, reduce inflammation in the blood vessels, and aid blood sugar control.

But until clinical trials help show whether vitamin D works, Sun advised people to stick with the tried-and-true ways of protecting their hearts: maintaining a healthy weight, getting regular exercise, eating a well-balanced diet and not smoking.

“There are many established ways to lower your cardiovascular disease risk,” Sun said. “People can focus on those measures.”

As for vitamin D, the sun is the major natural source, since sunlight triggers vitamin D synthesis in the body. Food sources are relatively few and include fatty fish like salmon and mackerel, and fortified dairy products and cereals.